1. Field of the Invention
This invention generally relates to a cap member. More specifically, the present invention relates to a cap member for an internally geared bicycle hub.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle cap member.
An internally geared bicycle hub generally includes a hub axle configured such that it can be mounted to a frame of a bicycle, a generally cylindrical driver mounted on the hub axle in such a fashion that it can rotate freely, a generally cylindrical hub shell arranged around the outside circumference of the hub axle, and a transmission mechanism having a plurality of power transmission paths and configured to transmit rotation of the driver to the hub shell through any one of the power transmission paths. A known method for preventing the penetration of moisture into the internally geared hub is to provide a moisture resistant cap member between the driver and the hub shell (e.g., Japanese Patent No. 3428559). A conventional cap member includes an annular housing and a seal member that is held by the annular housing and arranged and configured to touch against the driver. The annular housing has a cylindrical side wall and a seal connecting wall that extends radially inward from the side wall. Several of slots are formed in the side wall in such a fashion as to be arranged along a circumferential direction of the side wall. A connecting protrusion is also provided on the internal circumferential surface of the side wall, the connecting protrusion being arranged near the axially inward end of the side wall and configured to protrude slightly in the radially inward direction. The connecting protrusion is divided into sections by the slots and configured such that it can engage with a connecting groove formed in the external circumferential surface of the hub shell. With this design of cap member, the cap member is secured such that it will not fall off by the elastic engagement of the connecting protrusion with the connecting groove. When this kind of cap member is mounted on the end of a hub shell, a side portion of the hub shell is covered by the side wall and the seal connecting wall and it becomes more difficult for liquids to penetrate the gap between the hub shell and the driver because the seal member touches against the driver.
With the conventional design of cap member just described, the cap member and the hub shell are not mated closely together because the cap member is secured to the hub shell by the elastic engagement of the connecting protrusion (which is divided into sections by the slots) with the connecting groove. Consequently, there is the possibility that a gap that communicates with the outside of the hub shell will form between the hub shell and the cap member and allow liquids to penetrate to the inside of the hub. In order to prevent the penetration of liquids in hubs having such a conventional cap member, grease or other supplementary material or auxiliary member is applied or installed to the inside of the cap member to improve the moisture resistance.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for a cap member for an internally geared bicycle hub. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.